Solution mining of kcl-nacl with solvent at ambient temperature



Oct. 22, 1968 R- L. EVERY ET AL SOLUTION MINING OF KCl-NqCJZ WITH SOLVENT AT AMBIENT TEMPERATURE Filed Jan. 19, 1967 3 400 PARTS EiOH 70F 5 FROM s PARTS NoCL PARTS Nucl- CAVITY PARTS KCL 4 HLTER FILTRATEI so PARTS KCL PARTS 6/ 323 5231? I000 PARTS BRINE PPT.I 6

9 249 PARTS il 12s PARTs NoCL T M VACUUM DIST. m PARTS KCL 74 PARTs KCL A s E MM Hg 402 PARTs H20 20 mm ETOH '[Q'F 2l- 200 F 20 PARTS 32 STEAM 5 Io PPT. u 18 v FILTRATE u v F BOTTOMS II I PARTS NoCL 'F 22 13s PARTS KCL PARTS 402 PARTS H2O 33522123 0 we PARTS NoCL 35 640 PARTS BRINE l0 PARTS NuCL 12s PARTS NuCL 25 3] 27 o MAKE-UP FORMULA 70F 59.3 PARTS H2O TO 70F REPLACE NcICL 121 PARTs NoCL ITI PARTS 74 31.5 PARTS H 0 To 6| PARTs KCL PARTS 6 use 2 30 402 PARTS H20 REPLACE KCL PARTS "2 FILTER 97 PARTS H2O REG.

20 PARTS ADDED 77 PARTS H3O T0 PPT.

I3 77 PARTS REG.

T0 CAVITY AT 70' F PRODUCT 74 PARTS 00 PARTS NoCL 30 PARTS KCL 785 PARTS H20 2395 PARTS INJECTED INVENTORS RICHARD L. EVERY D'ARCY A. SHOCK A TTORA/EY 3,407,004 SOLUTION MINING F KCl-NaCl WITH SOLVENT AT AMBIENT TEMPERATURE Richard L. Every and DArcy A. Shock, Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Delaware 7 I Filed Jan. 19, 1967, Ser. No. 610,401

10 Claims. (Cl. 299--) ABSTRACT or THE DISCLOSURE Brine solution understaturated with respect to NaCl and KCl is injected at ambient temperature to subterranean formation of KC1-NaCl where KCl-NaCl is dissolved, the solution is returned to the surface where salt is precipitated byuse of precipitating liquid such as ethanol and solvent recovered by steam washing and KCl recovered by subjecting the solvent-free salt to a thermal cycle.

Background Potassium has long been recognized as a valuable ingredient in fertilizer and most such potassium is mined as the chloride. Unfortunately, potassium chloride is seldom found deposited except in association with other salts, particularly sodium chloride. Since sodium chloride is known to be harmful to plant life, it is necessary to separate the KCl from the NaCl. It is also known that deposits of NaCl and KCl are often found in subterranean formations some distance beneath the earths surface. Tunnel and pillar mining have been widely used to recover KCl from such deposits; however, since these salts are water soluble, a great deal of attention has been given to solution mining methods such as by drilling one or more bore holes into the formation and circulating water into the formation and recovering brine therefrom. It is also known that NaCl is substantially as soluble in cold water as in hot water whereas, KCl is substantially more soluble in hot water than in cold water. Therefore, most of the prior art methods of solution mining have involved pumping large quantities of hot water into the formation and returning the hot brine to the surface where said brine is cooled, precipitating out KCl. As the cavity increases in size, more and more hot water must be pumped into the cavity and elaborate means have been devised to keep the brine hot and to maximize the contact of the cavity walls with the hot water or brine.

It is apparent that a great amount of energy must be expended by such methods and therefore the economics of solution mining has not been as attractive as it would first appear.

Summary of invention According to this invention, water undersaturated with respect to NaCl and KCl is pumped at ambient temperatures into a subterranean salt formation wherein KCl and NaCl are dissolved, the resulting enriched brine is returned to the surface and treated with a precipitating agent, washing the precipitated salts free of precipitating agent and subjecting the washed salts to an aqueous thermal cycle to recover KCl from the KCl-NaCl mixture.

The drawing The drawing is a block flow diagram and material balnited States Patent() ance of a typical KCl recovery system according to the method of this invention.

Description of the invention KCl in association with NaCl in a subterranean formation will have one or more bore holes drilled into it. In case of a single bore hole, two pipes, usually arranged concentrically are cemented into place in the formation and brine undersaturated with respect to the salt is pumped into the formation via one such pipe and brine of increased concentration is removed via the other pipe. Preferably, the injection pipe will extend to a lower level than will the recovery pipe since the lower concentrated brine is lighter in weight and will rise up through the solution in the formed cavity thereby helping to keep the solution from becoming static near the cavity walls. However, this is not critical to the present invention. Where two or more bore holes are drilled into the formation, a fracture is initiated between bore holes and one or more bore holes will be used for injecting the undersaturated brine and one or more different bore holes will be used to recover the enriched brine. In both cases, it is desirable to keep the residence time of the brine of sufficient duration that it will be substantially saturated when it is returned to the surface 'for recovery of KCl. As has been indicated, the injection brine is at approximately ambient temperatures; however, no particular cooling or heating means are employed and the temperature may vary somewhat as will be obvious in the detailed description to follow. This temperature will generally be in the mango Gil- F. After the brine has reached'the desired degree of saturation in the cavity, it is brought to the surface and treated with a precipitating solvent such as low molecular weight alcohols, ketones, amines and the like. These solvents decrease the solubility of the salts in water and consequently KCl and NaCl will precipitate. The precipitate will be separated from the solution, steam washed free of solvent, and the solvent-free salt is then subjected to a thermal cycle to recover KC]. The initial filtrate and the steam and solvent from the steam wash are combined and vacuum distilled or decanted to recover solvent for recycle to the precipitation step. The remaining, solvent-free solution is recovered for recycle to the salt deposit. The solvent-free precipitate is dissolved in H O at an elevated temperature, generally ISO-300 F., using only sufficient water to dissolve the KCl at the selected temperature. All the NaCl will not go in solution and will be separated and removed. The solution is then cooled and since the temperature of the water has little effect on the solubility of NaCl, only KCl will precipitate. 'Dhis KCl is separated by filtration, and the filtrate is mixed with original solvent free precipitate to dissolve the K01 at the selected temperature.

While any solution depressants which can be separated from the brine can be used, we have found alcohols, amines, ketones, and the like especially useful, and we prefer the low molecular weight alcohols say of 1 to 6 carbon atoms. These low molecular weight alcohols are recovered by vacuum distillation and condensed whereas the amines and ketones generally employed form a separate liquid phase which can be recovered by decantation.

The precipitating solvent, or solution depressant, includes, but is not limited to: methylidethylamine, n-amylamine, diethanolamine, methylethylketone, methanol, ethanol, isopropanol, butanol, hexanol, ethylcnediamine,

allyl alcohol, Z-pentanol, 1,7-heptanediol, tertiary butyl alcohol, erythritol, arabitol, 1,4-pentanediol, cyclohexanol and the like. Mixtures of such materials can sometimes be used to advantage.

From the above examples, it can be seen that the precipitating solvent can be aliphatic, cyclic, aromatic, saturated or unsaturated and can have one or more functional groups, e.g., mono, di, or more functional groups.

In general, the amount of additive will depend upon the particular additive and its solubility; however, 2 to 100 volumes of additive per 100 volumes of brine will suffice, preferably 10 to 50 volumes of additive per 100 volumes of brine will be used. The temperature of the additive is not critical, and will generally be at or near ambient temperature.

The low molecular weight alcohols are generally readily available at low cost and are'therefore preferred.

To more clearly describe the invention, a typical KCl recovery process will be described using as a base, 1000 parts of brine from the solution cavity and ethanol as the precipitating solvent. We will assume 70 F. operating temperature. Since the removal of salt will increase the volume of the cavern, makeup water is utilized to fill this void. A formula for calculating the necessary makeup water is included wherein specific gravities of 2.16 and 1.98 for sodium chloride and potassium chloride, respectively, are assumed.

Referring now to the drawing, 1000 parts brine at 70 F. containing 208 parts NaCl, 104 parts KCl and 688 parts H O (all parts are by weight) are withdrawn from a cavity, not shown, via conduit 1 and passed to mixing zone 2 where it is mixed with 400 parts ethanol supplied through 3. The ethanol causes 128 parts NaCl and 74 parts KCl to precipitate, and the slurry is passed via conduit 4 to filter 5 wherein the precipitate containing some ethanol is separated from the solution. The filtrate is passed via conduit 6 to vacuum distillation zone 8 where it is mixed with steam and ethanol introduced via conduit 9 from source hereinafter described. Material balance of the filtrate stream in conduit 6 is shown in block 7. Since a portion of the alcohol remains with the precipitate, the material balance shows the ethanol to be less than 400 parts. In the instant case, vacuum distillation zone 8 is operated at 50 mm. Hg and 70 F. The ethanol is distilled off and sent to zone 2, previously described, via conduit 3.

The bottoms from distillation zone 8 pass via conduit 10 to makeup zone 12. The bottoms material balance is shown in block 11. The makeup formula is shown in zone 12 and shows 77 parts water will be required which is supplied via conduit 13. This adjusted brine solution is then passed to the cavity, not shown, via conduit 14. lock 15 shows the material balance of the injection brine.

The precipitate from filter 5 passes via conduit 16 to wash zone 17 where excess ethanol is removed with 20 parts steam supplied via conduit 18. This 20 parts steam is taken into account in the calculations in zone 12. The steam containing the ethanol is passed to distillation zone 8 via conduit 9 as previously described.

The washed precipitate from zone 17 passes via conduit '19 to zone 20 where it is mixed with additional brine, from source later disclosed via conduit 21, at sufficient temperature to provide a solution and NaCl precipitated at 200 F. The material balance is shown in zone 20.

The solution is separated from the NaCl precipitated in zone 20 and passed via conduit 22 through cooler and conduit 24 to precipitating and filter zone 26. The material balance of this filtrate is shown in block 23. The temperature of the filtrate is lowered from 200 F. to 70 F. in cooler 25 causing 74 parts KCl to precipitate. Since the cooler H O will hold more NaCl, additional NaCl is introduced via conduit 27 from source later described. The KCl precipitate from zone 26 is passed via conduit 28 to product storage 29. The material balances are again shown in each zone. The filtrate from zone 26 is passed via conduit 30, heater 32 and conduit 21 to zone 20 where it is mixed with the washed precipitate from zone 17 as previously described. The material balance of the filtrate from zone 26 is shown in block 31.

The NaCl precipitate from zone 20 is withdrawn via conduit 34 with excess NaCl being removed via conduit 33 and the makeup NaCl for zone 26 passing to said Zone 26 via conduit 27. The material balance of precipitated NaCl is shown in block 35.

In describing this invention, conventional pumps, valves, controls, etc. are omitted as they can readily be supplied by those skilled in the art. Also, for simplicity of description, process procedures are shown as occurring in separate zones. It will be obvious that these several steps can and, in many cases, will be carried out in the same vessel. For example, the ethanol can be added to the saturated brine from the cavity in the filter, the filtrate separated from the precipitate and the precipitate washed on the filter plates in a batch-type operation. In such a case, parallel filter streams could advantageously be employed. Alternatively, a drum filter utilizing a doctor blade to remove the precipitate can be operated continuously and the precipitate stream washed in a separate vessel. As another example, instead of using heater 32, zone 20 can be equipped with a steam jacket or heating coils to maintain the desired 200 F. Those skilled in the art will readily see other modifications which can be made. As previously pointed out, the material balance is based on an assumed ambient temperature of 70 F. and a thermal cycle of 200 F. With other temperatures, these balances will change as will be readily obvious to the skilled worker, and the balance can be readily determined by ascertaining from solubility tables or experimentation the solubility of the salts at various temperatures.

We claim:

1. In the solution mining of potassium chloride in association with sodium chloride with Water undersaturated with respect to these two salts, the process comprising passing said water to a subterranean formation at substantially ambient temperature wherein said water (brine) becomes more saturated with respect to the salts, returning the more highly concentrated brine to the earths surface, adding a liquid solubility depressant to the brine causing a portion of sodium chloride and potassium chloride to precipitate out, separating the precipitate from the remaining liquid, dissolving the potassium chloride with brine of relatively high temperature to form a concentrated solution thereof, separating the resulting liquid from any undissolved sodium chloride, cooling the resulting liquid to substantially ambient temperatures causing potassium chloride to precipitate and recovering the potassium chloride precipitate from the liquid.

2. The process of claim 1 wherein the solubility dcpressant is a water-soluble organic compound selected from the group consisting of alcohols, ketones and amines.

3. The process of claim 2 wherein the solution recovered from the first said precipitation step is fractionated to recover the organic solubility depressant from brine, returning the organic compound to the precipitation step and recirculating the brine to the subterranean formation along with makeup water.

4. The process of claim 3 wherein the brine from the potassium chloride precipitation step is utilized to dissolve the KCl from the first precipitation step and a portion of the undissolved sodium chloride is added to the cool brine in the potassium chloride precipitation step to concentrate the brine in respect to sodium chloride.

5. The process of claim 4 wherein the brine injected into the subterranean formation has a temperature in the range 60 to F., and the first precipitated salts are dissolved at a temperature in the range to 300 F.

6. The process of claim 5 wherein the amount of organic compound added to the brine from the subterranean formation is in the range 2 to 100 volumes per 100 volumes brine.

7. The process of claim 6 wherein the amount of organic compound added to the brine from the subterranean formation is in the range 10 to 50 volumes per 100 volumes of brine.

8. The process of claim 7 wherein the organic compound'is an alcohol of 1 to 6 carbon atoms.

9. The process of claim 8 wherein the organic compound is ethanol.

10. The process of claim 7 wherein the organic compound is diethanolamine.

References Cited UNITED STATES PATENTS 2,665,124 1/1954 Cross. 3,215,471 11/1965 Gunning. 3,262,741 7/ 1966 Edmonds et a1.

FOREIGN PATENTS 509,857 2/ 1955 Canada. 1,278,326 10/1961 France.

ERNEST R. PURSER, Primary Examiner. 

